Pop the popcorn according to the instructions and empty into a large bowl (be sure to remove any unpopped kernels).
Mix the corn syrup and brown sugar together in a microwave safe bowl and microwave on hight for 3 minutes.
Stir butter and vanilla into the brown sugar/syrup mixture and stir until the butter is melted.
Pour over the popcorn and stir until thoroughly coated.
Spread on cookie sheets (greased or sprayed with cooking spray) and dry until desired hardness. (When hard, I break it up a little more as I put it into the serving bowl to make it truly bite sized.).
Prep time includes time to pop popcorn (about 3 minute per bag - I usually measure out everything else while the popcorn's popping). Cooking time includes mixing but does not include drying time; however, that will vary depending on how hard you want your popcorn. We have a tendency to eat it pretty much right away!